Non-destructive tests for distinguishing between objects formed of dissimilar metals



Unitgd Slims P tent'O NON-DESTRUCTIVE TESTS FOR DISTINGUISH- .ING BETWEEN omncrs FORMED ornrssnn- LAR METALS John Danaczko, 'Jr., Oak Park, 111., assighorto Western Electric Company, Incorporated, New York, N.Y., a corporation of New York No Drawing. Filed July 11, 1958, Ser. No. 747,838

2 Claims. (Cl. 23-230) This invention relates to non-destructive methods of distinguishing between articles formed of dilferent metals having similar physical appearances, and more particularly to a non-destructive test for distinguishing between relay contacts formed of silver or palladium.

In designing contacts for electromagnetic devices, such as relays, problems, such as contact resistance and contact wear, are encountered and must be solved. When the problem is contact resistance, silver contacts are normally used in order to take advantage of the extremely high conductivity of silver. When the problem is contact wear, palladium is frequently used as the contact forming material because palladiums ability to resist wear substantially exceeds that of silver. Frequently, because of the specific circuitry involved, it is desirable to include both silver and palladium contacts in a single relay. When the relay is completely assembled, it is desirable to be able to ascertain whether the silver and palladium contacts have been properly locked in the relay structure. Since silver and palladium both present similar physical appearances, any test involving visual techniques will not suffice. It goes without saying, of course, that a suitable test technique must be one which is non-destructive.

It is therefore a primary object of this invention to provide a non-destructive process for distinguishing between articles formed of dissimilar metals.

It is another object of this invention to provide a nondestructive test process for distinguishing between articles formed of dissimilar metals which present similar physical appearances.

It is a further object of this invention to provide a non. destructive method of distinguishing between relay contacts formed of silver or palladium.

With these and other objects in view, the present invention contemplates a method including the steps of rubbing the contacts to be identified on an abrasive surface until marks caused by the deposition of minute quantities of the contact metals appear thereon and then treating these marks with an aqueous solution of ammonium hydroxide and ammonium persulfate, The aforementioned solution will dissolve the marks created by silver contacts, while leaving untouched those marks caused by the palladium contacts, thus distinguishing between the two.

A specific example of a method by which the invention has been successfully practiced is as follows. A sheet of filter paper was immersed in an aqueous suspension of a polishing grade of alumina and then permitted to dry to form an abrasive surface thereon. The filter paper was then brushed to remove the excess alumina from the surface. Although filter paper and polishing grade alumina have been described here, various other types of paper or cloth and various other abrasives of polishing grade may also be used. It is necessary that the materials used be such that they will not react in any. manner with the reagent. Next, 2.5 grams of chemically pure ammonium persulfate were added to 5 cc. of distilled water and stirred until the salt had been completely dissolved. Tap water or well water may also be utilized M 2,981,607 Patented Apr. 25, 11961 although distilled water is preferred. Finally, 2.5 cc. of chemically pure ammonium hydroxide were added to the salt solution and thoroughly mixed therewithto. complete the preparation of the reagent.

A set of .relay contacts of known compositions was then rubbed on the surface of the abrasive impregnated filter paper until each of the contacts had produced a mark thereon. Each of the marks was then treated with several drops of the aforedescribed reagent. After a few minutes, the marks caused by the silver contacts had completely disappeared, whereas those caused by the palladium contacts persisted indefinitely.

The chemical reactions which take place to effect the above results are as follows:

In reaction No. 1 above, the silver reacts with the ammonium persulfate in the presence of water to yield silver oxide, ammonium sulfate and sulfuric acid. This reaction is relatively slow; taking perhaps two or three minutes. As soon as the silver oxide has been produced by reaction No. 1, reaction No. 2 immediately takes place. In reaction No. 2 the silver oxide reacts with the ammonium hydroxide to yield water and a colorless soluble silver ammonia complex. The entire test takes several minutes because all of the silver is not immediately converted to silver oxide in accordance with the relationships in reaction No. l.

Reaction No. 3 is a side reaction which. has no effect upon the outcome of the test, but is set forth because it does in fact occur due to the particular constituents of the reagent. As soon as reaction No. 1 produces any sulfuric acid, it is immediately neutralized by some of the ammonium hydroxide which is present in the reagent; the results of this reaction being the production of ammonium sulfate and water.

A reagent which has been found to be eminently suitable for distinguishing between silver and palladium relay contacts comprises the following constituents present in quantities within the ranges stipulated:

Ingredients: Parts by weight, percent Distilled water, H O 25-50 Ammonium persulfate, (NH S O 20-40 Ammonium hydroxide, NH4OH 20-50 Deviation from the above range is possible, but not desirable because of the adverse effects (e.g., too long, incomplete, etc.) upon the practicability of the test.

It is to be understood that although the method described herein is utilized to distinguish between silver and palladium relay contacts, its utility is not limited thereto. It is obvious that the method disclosed herein is readily adaptable to other processes involving other articles formed of various metals. Additionally, it is manifest that modifications other than those suggested above may be made to the disclosed method to achieve a similar process which still embodies the principles of the present invention and which is within the spirit and. scope thereof.

What is claimed is:

1. A non-destructive method of distinguishing between articles of silver or palladium which comprises the steps of rubbing the articles on a sheet of alumina-impregnated filter paper until visible marks appear thereon, and then treating said visible marks with a solution containing by weight: 25 to 50 percent distilled water, 20 to 40 percent (NH S O and 20 to 50 percent NH OH whereby the visible marks caused by the silver articles will be dissolved while those caused by the palladium articles will remain unchanged.

2. A non-destructive method of distinguishing between solved while those caused by the palladium articles will articles of silver and palladium which comprises the steps remain unchanged. of immersing a sheet of filter paper in an aqueous suspension of aluminum oxide, allowing said filter paper to References Cited in the file of this Patent dry to form an abrasive surface thereon, rubbing articles 6 Feigl: Spot Tests, ed., 1954, p. 382.

of unknown characteristics on said alumina-impregnated w m Mik hemie, vol, 34, 192-195 (1949) abrasive surface until visible marks appear thereon, and V Ra d ll; J, Am. Chem. Soc vol. 52, pp. 178-191, then treating said visible marks with a solution containing 1930. V

by weight: 25 to 50 percent distilled water, 20 to 40 per- Underwood: Anal; Chemistry, vol. 24, 1952, pp.

cent (NH S O and 20 to 50 percent NH OH, whereby 10 1597-1601. the visible marks caused by the silver articles will be dis- 1. :Hig'son: .J Chem. 0 V01 PP- 2039-55, 1921- 

1. A NON-DESTRUCTIVE METHOD OF DISTINGUISHING BETWEEN ARTICLES OF SILVER OR PALLADIUM WHICH COMPRISES THE STEPS OF RUBBING THE ARTICLES ON A SHEET OF ALUMINA-IMPREGNATED FILTER PAPER UNTIL VISIBLE MARKS APPEAR THEREON, AND THEN TREATING SAID VISIBLE MARKS WITH A SOLUTION CONTAINING BY WEIGHT: 25 TO 50 PERCENT DISTILLED WATER, 20 TO 40 PERCENT (NH4)2S2O8, AND 20 TO 50 PERCENT NH4IH WHEREBY THE VISIBLE MARKS CAUSED BY THE SILVER ARTICLES WILL BE DISSOLVED WHILE THOSE CAUSED BY THE PALLADIUM ARTICLES WILL REMAIN UNCHANGED. 